This application relates to a unique method of controlling an unloader valve in a scroll compressor at shutdown to prevent unpowered reverse rotation.
Scroll compressors are becoming widely utilized in air conditioning and refrigerant applications. However, there are still design challenges facing scroll compressor designers. One persistent challenge with scroll compressor operation is unpowered reverse rotation at shutdown.
As known, scroll compressors consist of two interfitting and generally spiral wraps. The interfitting wraps define compression pressure pockets. One of the wraps usually orbits relative to the other and the size of the compression pockets change to compress an entrapped fluid. The orbiting scroll is driven by an electric motor via a shaft. On shutdown, when the power is turned off, there is no torque applied by the motor and the orbiting scroll can start rotating in reverse, as the high pressure fluid from the discharge line and compressor discharge muffler is expanded back through the compression elements into the compressor suction. After the pressure is equalized, or nearly equalized, the reverse rotation is stopped. Similarly, unpowered reverse rotation can occur if the fluid is expanded from an economizer line into the compressor suction through compression elements. This reverse rotation can create unwanted noise, and further can create other operational problems.
Thus, the prior art has attempted to reduce or eliminate the occurrence of unpowered reverse rotation. For the most part, the solutions to the unpowered reverse rotation problem have included the application of additional elements into the scroll compressor. One of the prior solutions was to use an internal compressor check valve which would close when high pressure fluid from the discharge line would rush back into the compressor after shutdown. The check valve blocked the high pressure fluid from entering the wraps and thus minimized the duration, or eliminated, unpowered reverse rotation. However, for compressors with an economizer circuit, the high pressure fluid can enter the compressor upstream of the check valve and still cause reverse rotation. Thus even the inclusion of additional costly internal elements as often used in the past would have not prevented unpowered reverse rotation of a scroll compressor with an economizer circuit.
Thus, it would be desirable to find a solution to the problem of unpowered reverse rotation that does not require any additional components to be added into the scroll compressor.